1. Field
The present invention relates to a consumable electrode type arc welding method, and particularly to an arc welding method which performs thick-plate welding by means of large current.
2. Description of the Related Art
(Current Increase/High Deposition in Arc Welding for Thick-Plate Work)
In arc welding for the work of such a thick-plate work that the thickness is 8 mm or more, increase of current and high deposition are demanded in order to improve efficiency and productivity of the welding operation. To meet such the demand, it is necessary to increase the welding-wire supplying amount per unit time as much as possible.
Therefore, methods of increasing the welding-wire feeding speed and further supplying the large current to the welding wire have been recently investigated.
In order to subject thick plates to high deposition, tandem welding in which the number of torches has been increased to the plural number is disclosed (for example, refer to JP-A-2004-243372).
In JP-A-2004-243372, measure of increasing the deposition amount by adding a torch to two torches, that is, by using three torches has been disclosed. The increase in the number of torches enables the electric current produced per torch to decrease, so that there are advantages that the strong magnetic field is not generated and the weld penetration does not become too deep.
Further, for thick-plate welding, a welding method has been disclosed in which a flux-cored wire or a metal-cored wire having the large diameter is used, and the amount of spatter is reduced by performing one-pass execution by tandem welding of a leading electrode and a trailing electrode by the welding current of AC (alternating current) 600 to 1900 A, or by performing multi-pass execution by a single electrode (for example, refer to JP-A-11-147175).
(Common Defects in Two Related Methods)
However, such the related arts, since the welding-wire feeding speeds are 7.5 m/min. in JP-A-11-147175 and 13 m/min. in JP-A-2004-243372, cannot meet fully the demand that high deposition is obtained by increasing the welding-wire feeding speed.
Further, in consumable electrode type arc welding by the large current, in case that the welding-wire feeding speed is increased, such a phenomenon is confirmed that the strong magnetic field is generated by the welding current thereby to cause the arc to start rotating and the wire tip rotates rapidly at a high speed with this arc rotation. For example, in MAG (Metal Active Gas) welding by means of a wire of 1.4 mm in diameter, in case that welding is performed in a state where the welding current exceeds 600 A and the welding-wire feeding speed is 25 m/min. or more, the arc starts to rotate. When the wire tip rotates at the high speed, the wire tip is brown off by the centrifugal force produced by the rotation and spatter is generated, so that welding itself becomes unstable.
On the other hand, in case that the arc length is decreased in order to reduce the influence of the arc rotation under the state where the current and welding-wire feeding speed are large, the arc power becomes strong, so that there is produced a problem that the weld penetration in the work formed by the arc power becomes too deep.
Neither of the related arts described in JP-A-2004-243372 and JP-A-11-147175 can respond to such the problems produced in the state where the current and welding-wire feeding speed are large.
(Another Defect in Method of JP-A-2004-243372)
Further, for such tandem welding as described in JP-A-2004-243372, it is extremely difficult to execute welding while keeping both of the leading electrode and the trailing electrode at the optimum posture for the welding portion including a curve. Therefore, the tandem welding is not easy to be applied to the work having many curves.
Further, since welding by the respective torches interfere with each other, special control for avoiding the interference between the torches is required. Furthermore, it is not easy to set the welding condition of each torch. Therefore, application of the plural torches to an automation line of welding has limitation.
(Another Defect in Method of JP-A-11-147175)
Further, in JP-A-11-147175, a combined wire such as a flux-cored wire or a metal-cored wire is used as the welding wire. Since these wires are more expensive than a solid wire, there is a problem in cost.